This invention relates generally to an automotive transmission or the like. More particularly, it relates to an anti-clash and anti-rattle brake for use in a multiple speed ratio manual transmission.
In recent years there have been many improvements in automotive drive trains, including improvements related to apparatus for shifting a manual transmission of the type incorporating a plurality of synchronized forward speed ratios and a non-synchronized reverse speed ratio. Such shift apparatus typically provides a plurality of crossover positions for a shift stick. Each crossover position selects a shift fork or lever which then may be moved to engage appropriate gears for establishing a particular speed ratio.
U.S. Pat. No. 4,337,675 issued July 6, 1982 discloses this type of shift apparatus. The patent is of common assignee herewith, and is incorporated herein by reference. The shift apparatus includes a shift stick which is movable in one plane to a plurality of neutral crossover positions, thereby rotating a shift rail about its longitudinal axis for speed ratio selection. The shift stick then is movable in another plane from each neutral crossover position, thereby sliding the shift rail along its longitudinal axis to engage appropriate gears for establishing the selected speed ratio. From a first neutral position gears may be engaged to establish the first or second forward speed ratio. From a second neutral position gears may be engaged to establish the third or fourth forward speed ratio. From a third neutral position gears may be engaged to establish the reverse speed ratio in a four-speed transmission, or the fifth forward or reverse speed ratio in a five-speed transmission.
To establish reverse, a non-synchronized reverse idler gear is slidable into meshing engagement with other gears in a reverse gear train. Typically at least one of these is synchronized, that is, rotating as part of a plurality of constantly meshed gears. In order to avoid gear clash, it would be desirable to brake the rotating gear before it is engaged by the reverse idler gear.
It would also be desirable to retard gear rattle by braking the constantly meshed gears when the transmission is in neutral, the clutch is engaged, and the engine of an associated vehicle is idling.
U.S. Pat. No. 4,294,338 issued Oct. 13, 1981 discloses shift apparatus including a modified synchronizer which functions as a countershaft brake. The patent is of common assignee herewith, and is incorporated herein by reference. Although this brake represents an advance in the art, it takes effect after crossover selection, that is, during gear-engaging movement of the reverse idler gear. It is known now that in some instances this is not soon enough to avoid gear clash. In any event, this apparatus does not provide an anti-rattle function.
U.S. Pat. No. 4,430,904 issued Feb. 14, 1984 discloses an anti-clash brake which takes effect during crossover selection, that is, prior to gear-engaging movement of the reverse idler gear. The patent is of common assignee herewith, and is incorporated herein by reference. This brake also represents an advance in the art. However, even though it takes effect during crossover selection, there are times when this too is not soon enough to avoid gear clash. It is clear now that in some instances the vehicle operator must pause briefly during the neutral-to-reverse shift to allow sufficient time for the brake to take effect. In addition, the braking effort continues when the transmission is engaged either in reverse or in any forward gear ratio which is engageable from the same crossover position as reverse. This contributes to excessive wear of the braking elements, and reduces transmission efficiency. Also, in the event of gear blockage during reverse engagement, additional friction makes completion of the operation difficult. Finally, this brake does not provide an anti-rattle function.
Thus there remains a need in the art for a simple, inexpensive brake which is effective before crossover selection to eliminate gear clash when a non-synchronized gear is to be engaged with a synchronized gear in a multiple speed ratio transmission. Further, it would be desirable for the brake to provide an anti-rattle function when the transmission is in neutral, the clutch is engaged, and the engine of an associated vehicle is idling.